Nucleic acid therapeutics have promise for treating diseases ranging from inherited disorders to acquired conditions such as cancer, infectious disorders (AIDS), heart disease, arthritis, and neurodegenerative disorders (e.g., Parkinson's and Alzheimer's). Not only can functional genes be delivered to repair a genetic deficiency or induce expression of exogenous gene products, but nucleic acid can also be delivered to inhibit endogenous gene expression to provide a therapeutic effect. Inhibition of gene expression can be mediated by, e.g., antisense oligonucleotides, double-stranded RNAs (e.g., siRNAs, miRNAs), or ribozymes.
A key step for such therapy is to deliver nucleic acid molecules into cells in vivo. However, in vivo delivery of nucleic acid molecules, in particular RNA molecules, faces a number of technical hurdles. First, due to cellular and serum nucleases, the half life of RNA injected in vivo is only about 70 seconds (see, e.g., Kurreck, Eur. J. Bioch. 270:1628-44 (2003)). Efforts have been made to increase stability of injected RNA by the use of chemical modifications; however, there are several instances where chemical alterations led to increased cytotoxic effects or loss of or decreased function. In one specific example, cells were intolerant to doses of an RNAi duplex in which every second phosphate was replaced by phosphorothioate (Harborth, et al, Antisense Nucleic Acid Drug Rev. 13(2): 83-105 (2003)). As such, there is a need to develop delivery systems that can deliver sufficient amounts of nucleic acid molecules (in particular RNA molecules) in vivo to elicit a therapeutic response, but that are not toxic to the host.
Nucleic acid based vaccines are an attractive approach to vaccination. For example, intramuscular (IM) immunization of plasmid DNA encoding for antigen can induce cellular and humoral immune responses and protect against challenge. DNA vaccines offer certain advantages over traditional vaccines using protein antigens, or attenuated pathogens. For example, as compared to protein vaccines, DNA vaccines can be more effective in producing a properly folded antigen in its native conformation, and in generating a cellular immune response. DNA vaccines also do not have some of the safety problems associated with killed or attenuated pathogens. For example, a killed viral preparation may contain residual live viruses, and an attenuated virus may mutate and revert to a pathogenic phenotype.
One limitation of nucleic acid based vaccines is that large doses of nucleic acid are generally required to obtain potent immune responses in non-human primates and humans. Therefore, delivery systems and adjuvants are required to enhance the potency of nucleic acid based vaccines. Various methods have been developed for introducing nucleic acid molecules into cells, such as calcium phosphate transfection, polyprene transfection, protoplast fusion, electroporation, microinjection and lipofection.
Cationic lipids have been formulated as liposomes to deliver genes into cells. In addition, cationic lipid emulsions have been developed to deliver DNA molecules into cells. See, e.g., Kim, et al., International Journal of Pharmaceutics, 295, 35-45 (2005).
Ott et al. (Journal of Controlled Release, volume 79, pages 1-5, 2002) describes an approach involving a cationic sub-micron emulsion as a delivery system/adjuvant for DNA. The sub-micron emulsion approach is based on MF59, a potent squalene in water adjuvant that is a component of commercially approved product Fluad®. 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) was used to facilitate intracellular delivery of plasmid DNA.
Yi et al. (Pharmaceutical Research, 17, 314-320 (2000)) discloses cationic oil-in-water emulsions that used soybean oil and DOTAP as the cationic lipid. Cholesterol, DOPE, and polymeric lipids were also included in some of the emulsions. The emulsions were shown to enhance the efficiency of in vitro transfection of DNA in the presence of up to 90% serum. The average size of the emulsion particles ranged from 181 nm to 344 nm, and the particle size increased after the emulsions were diluted in PBS buffer.
Kim et al. (Pharmaceutical Research, vol. 18, pages 54-60, 2001) and Chung et al. (Journal of Controlled Release, volume 71, pages 339-350, 2001) disclose various oil-in-water emulsions that were used to enhance in vitro and in vivo transfection efficiency of DNA molecules. Among the cationic lipids tested, DOTAP formed the most stable and efficient emulsion for DNA delivery. Among the oils tested, squalene, light mineral oil, and jojoba bean oil formed stable emulsions with small particles. The efficiencies of in vitro transfection were shown to correlate to the stability of the emulsions (e.g., the emulsion formulated by squalene at 100 mg/mL and DOTAP at 24 mg/mL showed high in vitro transfection efficiency). The emulsions were prepared by first mixing the cationic lipid with water to form a liposome suspension (by sonication). Liposomes were then added to the oil (such as squalene) and the mixture was sonicated to form an oil-in-water emulsion.
RNA molecules encoding an antigen or a derivative thereof may also be used as vaccines. RNA vaccines offer certain advantages as compared to DNA vaccines. However, compared with DNA-based vaccines, relatively minor attention has been given to RNA-based vaccines. RNAs are highly susceptible to degradation by nucleases when administered as a therapeutic or vaccine. Additionally, RNAs are not actively transported into cells. See, e.g., Vajdy, M., et al., Mucosal adjuvants and delivery systemsfor protein-, DNA-and RNA-based vaccines, Immunol Cell Biol, 2004. 82(6): p. 617-27.
Therefore, there is a need to provide delivery systems for nucleic acid molecules or other negatively charged molecules. The delivery systems are useful for nucleic acid-based vaccines, in particular RNA-based vaccines.